1. Field of the Invention
The present invention relates to a liquid supplying method for eventually supplying liquid to a liquid ejection head and to a liquid supplying device. In particular, the present invention relates to a system for supplying a liquid frequently used and to an ink jet recording apparatus equipped therewith.
2. Description of the Related Art
A recording head provided in an ink jet recording apparatus of this type can be mounted on a carriage which is fixed or reciprocated in a plane parallel to the recording material and in a direction perpendicular to the feeding direction of the recording material.
In such a scanning-type recording apparatus, the carriage is moved in a straight line by a predetermined command and, at the same time, ink droplets are ejected from the recording head in response to a predetermined signal to effect recording, and then the recording material is fed by a predetermined amount by a feeding device. These operations are repeated. Before or after image formation, the surface of the recording head on which ejection outlets are formed is capped to thereby effect a suction recovery operation, thereby keeping the ejecting section in the normal state.
The above-described recording head, which consumes ink when forming images, has to be constantly supplied with ink.
In one of the known methods for supplying ink to the recording head, an ink tank is provided at a position separate from the carriage and connected to the recording head through a tube. In this case, ink is supplied to the recording head by utilizing the head difference between the head and the ink tank.
In another method, a head cartridge is adopted, in which a negative pressure is generated in the ink tank with respect to the recording head to thereby detachably mount the ink tank on the carriage, forming the recording head and the ink tank as an integral unit. Such a head cartridge can be classified into two types: in one type, the recording head and the ink tank are constantly in an integrated state. In the other type, the recording head and the ink tank are formed as separate components, and both can be separated from the recording apparatus, the two components being united together when used.
The easiest way of generating such a negative pressure is to utilize the capillary action of a porous member (ink holding member). When this method is adopted, the ink tank includes a porous member such as a sponge accommodated for the purpose of storing ink and an atmospheric air communication opening for making it possible to take atmospheric air in the ink accommodating section to smooth the ink being used for printing.
To solve the problem of the porous member, which is rather poor in terms of ink accommodating capacity per unit volume, and to realize a stable ink supply, the present applicant has proposed in Japanese Unexamined Patent Publication No. 7-125232 a construction in which a porous member is inserted in a section of the ink tank.
FIG. 14 is a schematic sectional view showing an ink tank of the above-described construction. The interior of an ink tank 101 is divided into two spaces by a partition 103 having a communication hole 102. One space constitutes an ink accommodating chamber 104 which is tightly closed except for the communication hole 102 and which holds ink as it is without allowing it to come into contact with any other component. The other space constitutes an ink holding member accommodating chamber (atmosphere-communicating type liquid accommodating chamber) 106 for accommodating an ink holding member 105. In the walls defining this ink holding member accommodating chamber 106, there are formed an atmosphere-communication opening 107 for introducing atmospheric air as the ink is consumed, and a supply opening 108 for supplying ink to the recording head section. In this tank construction, when the ink of the ink holding member has been consumed by the recording head, air is introduced through the atmosphere communication opening into the ink holding member accommodating chamber and enters the ink accommodating chamber through the communication hole of the partition. As air is thus introduced, ink is fed from the ink accommodating chamber through the communication hole of the partition to fill the ink holding member in the ink holding member accommodating chamber. Thus, even when ink is consumed by the recording head, the absorbing member is filled with an amount of ink corresponding to the amount consumed, and the ink holding member holds a fixed amount of ink, keeping the negative pressure with respect to the recording head at a substantially constant level, whereby the ink supply to the recording head is stabilized. In particular, when, as in the case of Japanese Patent Unexamined Publication No. 6-40043, the passage for letting in atmospheric air is introduced and formed in the vicinity of the communicating section between the ink holding member accommodating chamber and the ink accommodating chamber, the ink supply can be effected in a more satisfactory manner.
In the above-described forms, whether they utilize head pressure or negative pressure, it is general practice for the ink tank to be replaced with a new one as soon as the ink has been used up. Hereinafter, this will be referred to as a "tank replacement system".
Another known ink supply system is a so-called pit-in system, in which a large-capacity tank for holding ink (hereinafter referred to as a "large tank") is provided and in which a head cartridge on which an ink tank and a recording head are integrally mounted is mounted on a carriage. The carriage is moved and the ink tank of the head cartridge (hereinafter referred to as the "tank section") is connected to the large tank at a predetermined position, whereby ink supply is effected. In this case, the ink tank constituting the tank section need not be replaced. Regarding the large tank, it is generally supplied with ink when all the ink therein has been consumed.
These conventional ink supply systems will be considered from the viewpoint of the supply of a frequently used ink. In the tank replacement system in which the head difference is utilized, it is necessary for the head difference between the tank and the recording head must be within a certain fixed range, so that an increase in the height of the ink tank is not possible. On the other hand, in the system adopting the form of head cartridge utilizing negative pressure, the cartridge is mounted on a reciprocating carriage, so that there is a limitation to the size of the ink tank. In either case, due to the limitation in tank size, the number of times that the ink tank is replaced increases in the case of a frequently used ink. Thus, these systems are disadvantageous from the viewpoint of stable ink supply.
On the other hand, those conventional systems in which ink is supplied to the tank section on the carriage, as in the case of the pit-in system, are not without their problems. In these systems, there is a variation in the ink level with respect to the space (volume) supplied with ink. Further, accurate supply of a fixed amount of ink is not possible. To overcome these problems, a system has been necessary in which any surplus amount beyond a predetermined amount of supplied ink is recovered (the overflow system), or a safety coefficient corresponding to the variation is used so that a very small amount of ink may be supplied. The former measure will lead to an increase in the size of the apparatus or waste of ink, and the latter measure will lead to an increase in non-recording period with the increase in the number of times that the ink supply is effected, resulting in a reduction in throughput.
The present invention has been made with a view toward solving the above problems in the prior art from a completely different point of view. It is a first object of the present invention to provide an ink supply system which can eliminate the above problems with a simple construction.
In the above-described conventional pit-in system, there is no need to replace the ink tank holding a frequently used liquid as in the case of the tank replacement system. However, when there are a plurality of such liquids, it is necessary to provide a plurality of large tanks corresponding to the tank sections accommodating these different liquids. In this case, there is a fear of wrong liquids being mixed with each other, i.e., color-mixing/liquid-mixing, if the wrong tank and the wrong tank section are connected to each other by an erroneous operation.
In particular, in some cases, before performing a predetermined recording in black ink, which is frequently used, the effect of fixing the color agent of the ink to the recording material is enhanced by processing the entire surface of the recording material with a processing liquid (hereinafter referred to as the "preprocessing liquid"). Such a processing liquid chemically reacts with the ink pigment to form insoluble matter (agents utilizing anion/cation reaction are known), so that, if the preprocessing liquid tank is connected with other tanks by erroneous operation, solidification will occur as a result of chemical reaction between the liquids, with the result that the ink tank, or in the worst case, even the recording head, become of no use. Thus, when the pit-in system in which a plurality of tank sections corresponding to the large tanks are provided is adopted, some measures must be taken to avoid color-mixing/liquid-mixing by erroneous operation.
Further, in the above-described pit-in system, when the construction in which the ink holding member is used as the negative pressure generating member in the tank section is adopted, supplying ink to the tank section from above results in a lot of time being required for the supplied ink to be supplied to the ink supply opening (usually provided in the lower section of the tank) to the head section. At the worst, air is allowed to enter the recording head to cause non-ejection.
In view of the above problems in the prior art, it is a second object of the present invention to provide a liquid ejection recording apparatus which adopts the pit-in system to reduce the number of times that the frequently used ink tank on the carriage is replaced is reduced, which prevents erroneous supply of different kinds of liquids, and which realizes a stable ink supply to the recording head.